This section is intended to introduce various aspects of the art, which may be associated with exemplary embodiments of the present invention. This discussion is believed to assist in providing a framework to facilitate a better understanding of particular aspects of the present invention. Accordingly, it should be understood that this section should be read in this light, and not necessarily as admissions of prior art.
There was never a shortage of challenges facing the offshore industry in deep-water or arctic frontiers. Nowadays, however, the challenge is particularly daunting with the merger of the two frontiers in new arctic deep-water leases, such as the Beaufort Sea, Chuckchi Sea, Kara Sea and elsewhere. These regions typically accumulate extreme amounts of ice during a majority of the year. Even when sheet ice is not present, these Arctic regions often face drifting ice floes. The industry is aware of substantial reserves of hydrocarbons present in such regions, particularly in areas below relatively shallow waters.
Due to the increased interest in oil and natural gas exploration in these regions, consideration is first given to conventional drilling platforms. These, however, are not suitable for the adverse conditions because of their inability to withstand ice loads. Without the proper precautions and designing, drifting ice presents high-levels of risk to the drilling units.
However, known drilling units designed for application in the Arctic and other ice-heavy environments have a variety of issues. One known technique may be collectively referred to as artificial islands and barges. These structures have typically been used in very shallow waters, such as 10 to 15 m. These artificial islands and barges have been utilized in the Canadian, Caspian Seas, to name an example. Unfortunately, their use beyond these water depths is typically impractical and cost-prohibitive, besides their potential environmental impact. Moreover, artificial islands are purpose-built to drill only one well, hence they are not easily mobile.
Another concept utilizes a caisson-type gravity-base structure (GBS). The use of a GBS is typically suitable for shallow waters (20 to 40 m), and the GBS also exhibits significant lateral capacity to resist ice loads. However, due to their constant height, these concepts cannot accommodate a range of water depths. Therefore, that precludes them from providing a constant water clearance which hampers safe lifeboat evacuation
Jack-ups or fortified jack-ups may be applied in the Arctic. While these structures can provide a constant clearance in a range of water depth, they suffer from limited foundation and jack-up leg capacity that typically preclude them from drilling in significant ice conditions. Even in open water season, they may not be able to resist a drifting ice floe or iceberg which may be present even in that season.
Floating systems are designed for deeper water depths (such as 100-150 m). However, known floating systems are limited by their insignificant station-keeping capacity compared to drifting ice or iceberg demands. Hence, they are limited to open water season, and even then require the use of icebreakers and a well-thought ice management plan.
Lastly, variable seafloor conditions, including very soft clays, often occur at Arctic and other sites. GBSs are typically the platform of choice to resist harsh environmental conditions, such as, but not limited to, ice forces experienced in the Arctic. Concrete or steel skirts are generally used to provide extra resistance to prevent the GBS from sliding due to ice forces, but they are expensive to construct and they need to be specifically designed to match site specific soil conditions.
Thus, there is a need for improvement in this field.